High pressure gas diaphragm valves are used in a wide variety of applications. Depending on their use, diaphragm valves can be exposed to high and low temperatures, temperature fluctuations across a wide temperature range, high and low pressures, and corrosive liquids or gases.
In addition to being suited to such conditions, the diaphragm of a diaphragm valve needs to be flexible and durable. Durability is important as regularly replacing diaphragms is typically a logistically difficult and expensive procedure. In use, a diaphragm may not be readily accessible, making replacement difficult. In order to replace a diaphragm it is generally necessary to suspend operation of the plant or machine of which the diaphragm is part. In some applications, especially those which require sterile or inert environments, diaphragm failure can contaminate the batch being produced and make it unsuitable for use.
Diaphragms are typically made, at least in part, from synthetic elastomers. One type of diaphragm consists of a central valve closure disk formed from a hard, inflexible material, such as metal, rigid plastic or a combination of metal and rigid plastic, supported on a flexible impervious fabric reinforced web. Such diaphragms are typically used in conjunction with a spring to ensure valve closure. The fabric may typically be nylon or the like. The fabric may be coated or laminated between sheets of Viton®, a fluoroelastomer available from DuPont Dow Elastomers, or Nitrile, also known as Buna-N, an acrylonitrile-butadiene copolymer. Both Viton® and Nitrile have good temperature and chemical resistance. However, such fabric reinforced diaphragms are subject to delamination and wicking of the nylon fibres, resulting in leakage and/or poor durability.
Moulded plastic diaphragms are an alternative to the fabric reinforced diaphragms. One moulded plastic diaphragm currently available is composed of Hytrel® (DuPont). Hytrel® is a thermoplastic polyester elastomer. However, Hytrel® is not suitable for use in applications where severe operating conditions may be experienced, as it has a low maximum operating temperature, approximately 60° C., a narrow range of chemical resistivity and is not particularly durable.
Moulded plastic diaphragms have also been made from high density polyethylene. These diaphragms are subject to early fatigue failure and are not resistant to high temperatures.
It would be desirable to provide a diaphragm that overcomes or ameliorates one or more disadvantages of existing diaphragms. Alternatively, it would be desirable to provide consumers with a useful choice.